The present invention generally relates to sliding caliper disc brakes, and particularly to a friction pad assembly therefor.
Sliding caliper disc brakes have been widely employed in a variety of automotive braking applications. For example, the Rath et. al. U.S. Reissue Pat. No. 30,255, entitled "Sliding Caliper Disc Brakes" reissued on Apr. 8, 1980, describes a particularly successful brake design, which is sometimes referred to herein as a "Colette" brake. This reissue patent is hereby incorporated by reference.
As described in the above-referenced patent, the disc brake includes a pair of opposing friction pad assemblies which are forced into engagement with a turning rotor or "disc" of the automobile wheel structure when the brake is applied to slow or stop the vehicle. A discussion of such friction pad assemblies may be found in Wienand et. al. U.S. Pat. No. 4,056,174, issued on Nov. 1, 1977, entitled "Friction Pad Assemblies For Sliding Caliper Disc Brakes" and Meyer et al U.S. Pat. No. 4,527,669, issued on Jul. 9, 1985, entitled "Friction Pad Assemblies For Use In Disc Brakes". Each of these patents are hereby incorporated by reference.
There are a number of significant considerations that may affect the design of a disc brake friction pad assembly. For example, the amount and direction of the force involved affect more than just the size of the friction pad assembly and the carrier or bracket that supports the friction pad assembly. In this regard, it should be appreciated that when the friction pad engages the rotor, substantial force will be brought to bear against the bracket by at least one abutment of the friction pad assembly. The direction of this force will be generally tangential to the arc created by the turning rotor. When a heavy braking force is generated, the bracket itself may deflect elastically, even though the bracket has substantial mass and strength. Accordingly, the application of a heavy braking force may have the effect of opening and changing the geometry of the area within which the friction pad assembly resides, and hence lifting the friction pad assembly off the bracket at the opposite or non-loaded end.
With a friction pad assembly having only a single upper abutment, a large reaction force will be borne by this abutment in high vehicle deceleration stops. Further, this large reaction force creates a large moment that must be reacted by the contact surface of the bracket at the opposite end of the pad. These large forces result in high bearing stresses which must be reacted by the pad and bracket. The size of the abutment bearing stresses can be reduced and the moment can be eliminated by the usage of a second, lower abutment or a large single abutment to share the reaction force. However, with dual abutments or a large single abutment, the angular deflection of the bracket which can occur during high deceleration stops can cause the non-loaded end of the friction pad assembly to lift away from the bracket. When the brake is released, the friction pad assembly may drop onto the bracket with an unwanted "clacking" noise. In this regard, it should be noted that a release of brake clamping pressure could cause the deflected arm of the bracket to act like a spring, and potentially accelerate the movement of the friction pad assembly back to its rest position.
Additionally, and importantly, it should be understood that the disc brake design needs to work effectively over extended periods of use. Thus, for example, the design of the friction pad assembly and the caliper should minimize the potential for unnatural wear to occur. Furthermore, the environment within which the disc brake has to operate is less than ideal. In this regard, the disc brake needs to accommodate the repeated presence of external contaminates, such as water, dirt, grease and salt, as well as contend with substantial swings in temperature.
Accordingly, it is a principal objective of the present invention to provide a friction pad assembly for a sliding caliper disc brake which is adapted to operate smoothly and effectively under heavy load conditions, such as when a substantial braking force is applied in an automobile or other wheeled vehicle.
It is another objective of the present invention to provide a friction pad assembly for a sliding caliper disc brake which avoids pad climbing or lifting during brake application or pad induced noise upon brake release.
It is a further objective of the present invention to provide a friction pad assembly for a sliding caliper disc brake which does not present corrosion concerns during extended periods of use in adverse environmental conditions.
It is an additional objective of the present invention to provide a friction pad assembly for a sliding caliper disc brake which will help to avoid undue wear, such as burnishing or indenting of the bracket.